1. Field of the Invention
The invention generally is related to a semiconductor structure and a method of making the same. More particularly, the invention is related to a high-k metal gate (HK/MG) semiconductor device that can avoid tungsten seam issues.
2. Description of the Prior Art
Continuing advances in semiconductor manufacturing processes have resulted in semiconductor devices with finer features and higher degrees of integration.
As the size of the integrated circuit devices continues to scale down, the polysilicon gate and the silicon dioxide insulating layer of a metal-oxide-semiconductor field effect transistor (MOSFET) structure have confronted with the physical limits of the materials themselves. To meet the demands of scalability, it is necessary to incorporate high-k metal gate (HK/MG) process.
Today, two main integration options remain: gate-first (often referred to as MIPS, metal inserted poly-silicon) and gate-last (also called RMG, replacement metal gate). The terminology “first” and “last” refers to whether the metal electrode is deposited before or after the high temperature activation anneal of the flow.
The RMG process typically involves a bulk tungsten filling process in a gate trench to form a low-resistance metal layer in the composite metal gate structure. After bulk tungsten filling, tungsten seams or voids are often observed in the bulk tungsten layer. Such tungsten seams are commonly exposed during subsequent chemical mechanical polishing (CMP) process, which results in electrical device degradation.
Therefore, there is a need in this technical field to provide an improved semiconductor structure such as a high-k metal gate semiconductor device without such tungsten seam issues.